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PubMed2006

Degradation of tetraphenylphosphonium bromide at high pH and its effect on radionuclide solubility.

Recently, tetraphenylphosphonium bromide (TPPB) has been used to remove technetium from some radioactive waste streams. However, before TPPB could be approved for use it was necessary to show that TPPB and its degradation products would not have a significant detrimental effect on post-closure performance of a radioactive waste repository. TPPB is known to be stable at neutral pH, however, under alkaline conditions it degrades by an alkaline hydrolysis mechanism to triphenylphosphonium oxide (TPPO). Degradation can also occur by radiolysis to produce triphenylphosphine (TPP). The kinetics of the alkaline hydrolysis degradation of TPPB is described and the solubility of europium, iodine, nickel, technetium(VII) and uranium(VI) in aqueous solutions of TPPB and its degradation products is reported. These results were used to support the use of TPPB in removing technetium from some waste streams.

Hydrolysis↗
PubMed1986

Incineration and monitoring of low-level 3H and 14C wastes at a biological research institution.

Low-level radioactive waste containing liquid scintillation fluid and known amounts of 14C and 3H has been incinerated in a modified pathological incinerator with the incinerator effluent, refractory surface and ash being monitored. The study relates the activity monitored to that incinerated and discusses how this relation was affected by a modification of the incinerator and monitoring conditions. No significant activity was found to be associated with the ash, particulates or the refractory surface. These data suggest that most of the activity is released as tritiated water vapor and 14C-labeled carbon dioxide. However, incomplete oxidation may occur for short periods of time depending on the amount of liquid scintillation fluid incinerated, with the possible release of 14C-labeled carbon monoxide.

Carbon Radioisotopes↗
PubMed1999

A perspective on nuclear waste.

The management of spent nuclear fuel and high-level nuclear waste has the deserved reputation as one of the most intractable policy issues facing the United States and other nations using nuclear reactors for electric power generation. This paper presents the author's perspective on this complex issue, based on a decade of service with the Nuclear Waste Technical Review Board and Board on Radioactive Waste Management of the National Research Council.

Geological Phenomena↗
PubMed2006

Application of a generic biosphere model for dose assessments to five European sites.

The BIOMOSA (BIOsphere MOdels for Safety Assessment of radioactive waste disposal) project was part of the EC fifth framework research programme. The main goal of this project was to improve the scientific basis for the application of biosphere models in the framework of long-term safety studies of radioactive waste disposal facilities and to enhance the confidence in using biosphere models for performance assessments. The study focused on the development and application of a generic biosphere tool BIOGEM (BIOsphere GEneric Model) using the IAEA BIOMASS reference biosphere methodology, and the comparison between BIOGEM and five site-specific biosphere models. The site-specific models and the generic model were applied to five typical locations in Europe, resulting in estimates of the annual effective individual doses to the critical groups and the ranking of the importance of the exposure pathways for each of the sites. Uncertainty in the results was also estimated by means of stochastic calculations based on variation of the site-specific parameter values. This paper describes the generic model and the deterministic and stochastic results obtained when it was applied to the five sites. Details of the site-specific models and the corresponding results are described in two companion papers. This paper also presents a comparison of the results between the generic model and site-specific models. In general, there was an acceptable agreement of the BIOGEM for both the deterministic and stochastic results with the results from the site-specific models.

Body Burden↗
PubMedDate not supplied

Civilian and military uses of depleted uranium: environmental and health problems.

Depleted uranium is a by-product of the process of enrichment of natural uranium and is classified as a toxic and radioactive waste; it has a very high density (approximately 19 g cm-3), a remarkable ductility and a cost low enough to be attractive for some particular technical applications. Civilian uses are essentially related to its high density, but the prevailing use is however military (production of projectiles). From the radioactive point of view, the exposure to depleted uranium can result from both external irradiation as well as internal contamination. The associated risks are however mainly of chemical-toxicological kind and the target organ is the kidney. In the present note the recent military uses and the possible effects of its environmental diffusion are discussed.

Animals↗
PubMed1998

Separation of radiolabeled orthophosphate and adenosine 5'-triphosphate by 20% polyacrylamide gel electrophoresis: an assay for brain microsomal Mg2+/Ca2+ ATPase activity.

Measuring orthophosphate is an important tool in biochemical analyses used to study membrane transport ATPases essential for calcium homeostasis. Current techniques involve extraction of radioactive phosphate with organic solvents, a technique that results in large quantities of hazardous radioactive waste. Other colorimetric assays are less sensitive and are complicated by interference of background absorbance from membrane tissue and unutilized ATP. This report describes a unique assay for the detection of inorganic phosphate and its application to the study of rat brain microsomal Mg2+/Ca2+ ATPase from a membrane fraction. The technique involves the separation of radioactive phosphate from unused gamma-radiolabeled ATP by resolution on 20% polyacrylamide gels. Both are visualized with X-ray film and quantitated by liquid scintillation counting after extraction from the gels. The assay can detect as little as 4.1 pmol of radiolabeled ATP and ATPase activity in 3.5 ng/microliter of membrane protein. This method offers the advantage of simultaneous quantitation of radiolabeled ATP and radioactive orthophosphate without the generation of large quantities of radioactive waste. The results demonstrate the development of a novel assay procedure for quantitating orthophosphate that is extremely sensitive, reproducible, and applicable to the study of any phosphate liberating enzyme.

Adenosine Triphosphate↗
PubMed2003

Quantification of the interaction of Tc with dissolved boom clay humic substances.

Technetium-99 (Tc), a fission product of uranium-238, is an important radionuclide because of its long half-life and its high yield in radioactive waste. To elucidate the Tc geochemical behavior in reducing environments relevant to geological disposal and in the presence of humic substances (HS), experiments were set up that resulted forthe first time in the determination of an interaction constant for Tc with dissolved humic substances. A number of lab-scale Boom Clay (a possible geological underground High-Level Radioactive Waste storage site in Mol, Belgium) batch experiments were set up, combining both different initial Tc(VII) concentrations and different solid/liquid ratios. On these batches several sequential extraction steps with HS-free synthetic Boom Clay water were performed. Equilibration times were fixed at 1 week for each extraction step. Tc(VII) was found to be readily reduced to Tc(IV) by the solid Boom Clay phase. This solid phase was able to sorb Tc(IV) to a very large extent (log Kd approximately 2.5-4.0), and two sorption sinks (one of which is humic substances) were detected. In solution, Tc(IV) was mainly associated with HS. Concentrations in solution were found up to the order of 2 x 10(-6) M. The results were quantitatively described as a competition for Tc(IV) between the solid phase and the dissolved HS (Schubert-like approach). It was concluded that a hydrophobic sorption of uncharged Tc(IV) species in solution would act as the dominating interaction mechanism with HS, with an interaction constant log K(HS) = 5.3 +/- 0.3.

Adsorption↗
PubMed1982

Extreme scenarios for nuclear waste repositories.

Two extreme scenarios for release of radioactive waste have been constructed. In the first, a volcanic eruption releases 1 km2 of an underground nuclear waste repository, while in the second, waste enters the drinking water reservoir of a major city. With pessimistic assumptions, upper bounds on the number of cancers due to radiation are calculated. In the volcano scenario, the effects of the water are smaller than the effects of natural radioactivity in the volcanic dust if the delay between emplacement and eruption exceeds 2000 yr. The consequences of the waste in drinking water depend on the survival time of the canisters and the rate of leaching of the nuclides from the waste matrix. For a canister life of 400 yr and a leach time of 6300 yr the cancer rate in the affected area would increase by 25%.

Air Pollution, Radioactive↗
PubMed1999

A physically based approach to modelling radionuclide transport in the biosphere.

Calculations of radiological risk are required to assess the safety of any potential future UK deep underground repository for intermediate-level and certain low-level solid radioactive wastes. In support of such calculations, contaminant movement and dilution in the terrestrial biosphere is investigated using the physically based modelling system SHETRAN. Two case studies are presented involving modelling of contaminants representing long-lived poorly sorbed radionuclides in the near-surface aquifers and surface waters of hypothetical catchments. The contaminants arise from diffuse sources at the base of the modelled aquifers. The catchments are characterised in terms of detailed spatial data for topography, the river network, soils and vegetation. Simulations are run for temperate and boreal climates representing possible future conditions at a repository site. Results are presented in terms of the concentration of contaminants in the aquifer, in soils and in surface waters; these are used to support the simpler models used in risk calculations.

Climate↗
PubMed2006

A mountain-scale thermal-hydrologic model for simulating fluid flow and heat transfer in unsaturated fractured rock.

A multidimensional, mountain-scale, thermal-hydrologic (TH) numerical model is presented for investigating unsaturated flow behavior in response to decay heat from the proposed radioactive waste repository in the Yucca Mountain unsaturated zone (UZ), The model, consisting of both two-dimensional (2-D) and three-dimensional (3-D) representations of the UZ repository system, is based on the current repository design, drift layout, thermal loading scenario, and estimated current and future climate conditions. This mountain-scale TH model evaluates the coupled TH processes related to mountain-scale UZ flow. It also simulates the impact of radioactive waste heat release on the natural hydrogeological system, including heat-driven processes occurring near and far away from the emplacement tunnels or drifts. The model simulates predict thermally perturbed liquid saturation, gas- and liquid-phase fluxes, and water and rock temperature elevations, as well as the changes in water flux driven by evaporation/condensation processes and drainage between drifts. These simulations provide insights into mountain-scale thermally perturbed flow fields under thermal loading conditions.

Computer Simulation↗
PubMed1996

125I aqueous waste volume reduction at a pharmaceutical research laboratory.

A wide variety of radioactive waste is generated by pharmaceutical research. One particularly high volume low specific activity waste stream produced by a research and development facility is aqueous 125I waste. This waste is generally held for decay and released to the sanitary sewer when the activity is low enough to ensure that concentrations are well below the appropriate regulatory limits. However, the large volume of this particular waste stream rapidly exhausted available space to store it for decay. This study investigated safe, inexpensive, and efficient methods for removing 125I from the aqueous waste, with the goal of implementing a practical process for concentrating the activity and thus reducing the stored volume. The implemented treatment (volume reduction) process used commercially available low cost activated carbon/particulate filters and inexpensive resin beds manufactured in-house. The much smaller volumes of spent filters and resin beds are then held for decay and eventual incineration. This technique has proven an effective means for managing this high volume waste stream.

Adsorption↗
PubMed1993

Monitoring of 35S in ash of incinerated waste.

The National Institute of Environmental Health Sciences incinerates low-level radioactive waste containing 3H, 14C, and 35S as a means of volume reduction. The primary isotope remaining in the ash is 35S. Some effects of the chemical and physical form of the waste on sulfur retention in ash and several methods for determining the activity remaining in the ash have been explored. It was found that the sulfur in sodium sulfate has a higher retention in ash than the sulfur in methionine and that the presence of glass appears to enhance the retention. Liquid scintillation and proportional counting methods were compared. A sulfur extraction procedure using liquid scintillation counting was found to give the lowest minimum detectable activity. However, it was determined that a more practical method for routine monitoring is to suspend a small quantity of ash in a liquid scintillation gel.

Environmental Monitoring↗
PubMed1986

A generic probabilistic risk analysis for a high-level waste repository.

A generic probabilistic risk analysis (PRA) is developed for high-level radioactive waste buried in a repository. The basic assumption is that an atom of buried waste has the same probability of escape as an atom of average rock at the same depth. Corrections are applied for variation of ground-water flow with depth, and for the fraction of ingested material derived from rock versus from soil. The final result is that we may eventually expect 0.012 deaths/GWe-yr. It is shown that this analysis is a PRA, and that the basic assumption is a conservative one--more likely to overestimate than to underestimate the hazard. This health impact is compared with those from other wastes generated in producing electricity.

Food↗
PubMed2006

Engineering of Deinococcus radiodurans R1 for bioprecipitation of uranium from dilute nuclear waste.

Genetic engineering of radiation-resistant organisms to recover radionuclides/heavy metals from radioactive wastes is an attractive proposition. We have constructed a Deinococcus radiodurans strain harboring phoN, a gene encoding a nonspecific acid phosphatase, obtained from a local isolate of Salmonella enterica serovar Typhi. The recombinant strain expressed an approximately 27-kDa active PhoN protein and efficiently precipitated over 90% of the uranium from a 0.8 mM uranyl nitrate solution in 6 h. The engineered strain retained uranium bioprecipitation ability even after exposure to 6 kGy of 60Co gamma rays. The PhoN-expressing D. radiodurans offers an effective and eco-friendly in situ approach to biorecovery of uranium from dilute nuclear waste.

Acid Phosphatase↗